This invention relates to an injector driving method, and more particularly to a method for driving an injector for feeding an internal combustion engine with fuel.
An injector used for feeding an internal combustion engine with fuel includes a valve for operating a fuel injection port and an electromagnet for driving the valve and is adapted to open the fuel injection port to feed fuel to the engine while a driving coil of the electromagnet is fed with a predetermined current.
For the purpose of driving the injector, a power circuit for applying a power supply voltage across the driving coil of the injector, an injection command signal generating section for generating an injection command signal of a predetermined signal width and a switch circuit connected in series to the driving coil of the injector are provided.
The injection command signal generating section is generally equipped with a microcomputer and has an output of a signal source including information on both an angle of rotation of the engine and an engine speed and outputs of various sensors such as a sensor for detecting a degree of opening of a throttle, a temperature sensor and the like inputted thereto, to thereby operate fuel injection time depending on a degree of opening of a throttle, a temperature, an atmospheric pressure, an engine speed and the like by means of the microcomputer, resulting in generating an injection command signal of a signal width corresponding to a predetermined fuel injection rate at a predetermined fuel injection start position.
The switch circuit connected in series to the driving coil of the injector is kept turned on while the injection command signal is generated, to thereby feed a driving current to the driving coil of the injector. Such feeding of the driving current to the driving coil of the injector causes the valve of the injector to be open when the driving current is increased to a predetermined level, to thereby start injection of fuel; whereas when the injection command signal is extinguished to stop feeding of the driving current to the driving coil, the valve is closed to interrupt injection of fuel. The internal combustion engine is fed with fuel in an amount determined by a product of a period of time during which the valve of the injector is kept open and a pressure of fuel fed to the injector.
Conventionally, a battery has been used as a power supply for a power circuit for driving the injector for the internal combustion engine. In addition, it has been recently considered, in order to permit the injector to be likewise applied to an engine for a vehicle, a ship or the like which is not mounted thereon with a battery, to use a power circuit in which a magneto driven by the engine is used as a power supply.
FIG. 12 schematically shows a conventional fuel injection device which was proposed by the assignee. In FIG. 12, reference numeral 1 designates a signal source, 2A is a main injection command signal generating portion, 2B is an auxiliary injection command signal generating portion, 3 is a power circuit, 4 is an injector for an internal combustion engine, 5 is a switch circuit connected in series to an exciting coil 4a of the injector 4, 2C is a switching circuit for feeding the switch circuit 5 with a trigger signal during a period of time for which the main injection command signal generating portion 2A generates a main injection command signal Vj or the auxiliary injection command signal generating portion 2B generates an auxiliary injection command signal Vj'. In the device of FIG. 12, the main injection command signal generating portion 2A, auxiliary injection command signal generating portion 2B and switching circuit 2C cooperate with each other to constitute an injection command signal generating section.
The signal source 1 is a signal generator including a rotor 101 mounted on a revolving shaft of the internal combustion engine and a signal generating element 102, wherein the rotor 101 includes a reluctor 101a arranged on an outer periphery of a rotator made of iron. The rotator for the rotor 101 may comprise a flywheel of a flywheel magnet rotating element mounted on the engine. The signal generating element 102 includes an iron core having a magnetic pole section arranged opposite to the rotor 101, a signal coil 1a wound on the iron core and a permanent magnet magnetically coupled to the iron core, as known in the art. A variation in magnetic flux occurring when the reluctor 101a starts to be opposite to the magnetic pole section of the iron core of the signal generating element 102 and such opposition of the reluctor 101a to the magnetic pole section of the iron core of the signal generating element 102 terminates causes pulse-like signals Vs1 and Vs2 to be generated on the signal coil 1a, respectively.
The main injection command signal generating portion 2A is realized by a microcomputer 200 driven by an output of the power circuit 3 and a predetermined software for operating the microcomputer and functions to operate fuel injection time based on an output of the signal source 1 and outputs of various sensors such as a throttle sensor for detecting a degree of opening of a throttle valve, a temperature sensor for detecting a temperature of air sucked, a pressure sensor for detecting an atmospheric pressure and the like which are inputted thereto, resulting in generating a main injection command signal Vj of a rectangular waveform at a fuel injection start position.
The auxiliary injection command signal generating portion 2B comprises a rectangular signal generating circuit 201 for generating a signal of a rectangular waveform such as a monostable multivibrator or the like and is adapted to be triggered to generate an auxiliary injection command signal Vj' of a rectangular waveform which has a predetermined time width, when the signal source 1 generates a predetermined signal.
The main injection command signal Vj and auxiliary injection command signal Vj' thus generated are then fed to the switching circuit 2C. A program for operating the microcomputer 200 has a check program for checking operation of the microcomputer according to a known procedure incorporated therein; so that when the microcomputer is under normal operation, it is permitted to generate a switching signal Ve of a high level, which is then fed to a control terminal of the switching circuit 2C. The switching circuit 2C comprises a relay or semiconductor switch and functions to feed a control terminal of the switch circuit 5 with an injection command signal Vjo during a period of time for which the microcomputer 200 is kept generating the main injection command signal Vj when the switching signal Ve is fed, to thereby turn on the switch circuit 5. The switching circuit 2C also feeds the control terminal of the switch circuit 5 with the injection command signal Vjo during a period of time for which the rectangular signal generating circuit 201 generates the injection command signal Vj'. The switch circuit 5 is kept turned on during a period of time for which it is fed with the injection command signal Vjo from the witching circuit 2C, so that a driving current Id may be fed from the power circuit 3 to the driving coil 4a of the injector 4. The injector 4 opens the valve when the driving current is increased to a predetermined level after it is fed thereto, resulting in carrying out injection of fuel into a fuel injection space of the engine. Normally, fuel is injected into a throttle body of the engine.
The power circuit 3 includes a generating coil 3a arranged in a magneto mounted on the internal combustion engine, a rectifier 3b and a power capacitor 3c charged through the rectifier 3b by means of an output of the generating coil 3a. A voltage Vc induced across the power capacitor 3c is applied to a power terminal of the microcomputer 200, across a series circuit of the driving coil 4a of the injector and the switch circuit 5, and to a power terminal of the rectangular signal generating circuit 201.
The fuel injection device generally requires a fuel pump for feeding fuel to the injector. The fuel pump is driven by means of an output of an additional generating coil provided on the magneto separately from the generating coil 3a. A pressure of fuel fed from the fuel pump to the injector is kept at a substantially constant level by a regulator.
The fuel injection device adapted to control fuel injection time by means of a microcomputer is disadvantageous in that a failure in normal operation of the microcomputer leads to a failure in operation of the engine. In particular, such a failure in operation of a microcomputer encountered during operation of an outboard motor, a snow mobile or the like brings on danger such as a failure in navigation, stalling in the snow or the like.
In view of the problem, the fuel injection device of FIG. 12 is provided with the auxiliary injection command signal generating portion 2B using a hardware circuit separately from the main injection command signal generating portion 2A using a microcomputer; so that when the microcomputer fails in normal operation, the injector may be driven by means of an injection command signal generated from the auxiliary injection command signal generating portion.
More particularly, in the fuel injection device of FIG. 12, the injector 4 is fed with a driving current during a period of time for which the microcomputer 200 generates the main injection command signal Vj when the microcomputer 200 is under normal operation, so that fuel injection time may be controlled by the microcomputer 200. When the microcomputer 200 fails to normally operate, the microcomputer stops generating the switching signal Ve, so that the switching circuit 2C feeds the switch circuit 5 with the injection command signal Vjo during a period of time for which the auxiliary injection command signal generating portion 2B generates the auxiliary injection command signal Vj'. Thus, in an emergency wherein the microcomputer fails in normal operation, the auxiliary injection command signal generating portion 2B functions to control fuel injection time.
As described above, when the injector 4 is driven by the power circuit 3 which uses, as a power supply therefor, the generating coil provided in the magneto mounted on the engine, charges in the power capacitor are discharged toward the injector during starting of the engine before charges in an amount required for driving the injector are accumulated in the power capacitor. This causes accumulation of charges required for driving the injector in the power capacitor to be delayed, resulting in much time being required for starting operation of the injector or opening the valve of the injector, leading to deterioration in starting characteristics of the engine.
Also, a fuel feed rate at which fuel is fed from the injector to the engine is determined by a product of a fuel feed pressure under which fuel is fed to the injector and fuel injection time for which the valve of the injector is kept open, whereas the fuel feed pressure is kept constant during operation of the engine. Thus, in driving of the injector, the fuel injection time is operated on the assumption that the fuel feed pressure is constant. However, driving of the fuel pump using the magneto as a power supply therefor requires much time to increase a discharge pressure of the fuel pump to a predetermined level after starting operation of the engine is started. Thus, driving of the injector for injection of fuel immediately after start of starting operation of the engine causes a fuel injection rate to be insufficient during initial injection of fuel. Substantial deficiency of the fuel injection rate during the initial fuel injection substantially affects starting characteristics of the engine as compared with some deficiency thereof.